Golf ball components are formed from a variety of compositions. For example, golf ball cores, intermediate layers, and covers may be formed from materials ranging from balata to ionomer resin to polyurethane or polyurea. Manufacturers constantly experiment with the different materials for use in the various golf ball layers in order to provide golf balls that have desirable aerodynamic properties, soft “feel”, and increased durability. Therefore, depending on the materials used to construct the golf ball components, the golf ball may have long distance, but poor durability, or have good durability, but a hard “feel”.
Golf balls function partly as a result of their ability to transfer kinetic energy of a moving golf club head to the golf ball. The ability to transfer this kinetic energy is related to the modulus of elasticity of the various polymeric compounds that make up the components of the golf ball in addition to the material properties of the golf club. Because the modulus of elasticity varies with temperature, high and low temperatures will typically effect the performance of the golf ball. In fact, the coefficient of restitution (COR), which is the ratio of the outbound or rebound velocity to the incoming or inbound velocity, may be used, at least in part, as an indicator of performance at various temperatures. And, as known to those of ordinary skill in the art, the COR of most golf balls decreases as the temperature of the environment decreases. Thus, golfers in cold climates may experience shorter driving distance and a “hard feel” due to the COR loss of the golf ball at non-optimal temperatures.
For practical purposes, the optimum temperature for maximum driving distance and a “soft” feel is about 59° F. to about 95° F. Depending on the season and the climate, golf balls can be well below this optimum temperature range. Generally, the higher the temperature within a given range, the higher the modulus of elasticity, and, conversely, the lower the temperature, the lower the modulus of elasticity. In other words, as the temperature drops, golf balls generally become stiff and usually cannot be driven as far as when they are warm. In fact, golf balls stored in an unheated area may have a ball temperature of 32° F. or less, which may have a dramatic effect on the driving distance and feel of the golf ball.
One way to avoid playing with a golf ball that has a temperature outside of the optimum range is to manufacture the golf ball with a qualitative temperature indicator. Examples of golf balls having such temperature indicators are disclosed in U.S. patent Publication No. 2003/0109329. Another way to compensate for non-optimum ball temperatures is to use a portable golf ball warmer, such as the one disclosed in U.S. Pat. No. 5,915,373.
Still another attempt at reducing the effect of non-optimal temperatures on driving distance and golf ball feel is to use a golf club that compensates for various changes in stiffness of a golf ball. U.S. Pat. No. 5,899,818 discloses a golf club head having temperature-variable impact properties using a shape memory alloy that becomes stiffer at higher temperatures and more elastic at lower playing temperatures. While these methods allow a player to use a golf ball in non-optimal playing conditions and may allow the golfer to achieve adequate distance, they require special equipment to do so.
Yet another known problem with conventional golf balls is the degradation of the materials used to form the golf ball components at elevated temperatures. For example, wrinkling of the golf ball component may occur at about 50° C. In fact, even the most advanced light stable polyurethane and polyurea compositions have been shown to be susceptible to heat degradation during additional processing steps, e.g., coating and marking, and upon storage in non-optimal temperatures.
With regard to material degradation at elevated temperatures, several manufacturers have attempted to compensate for any golf ball cover degradation upon application of heat by using coatings having contraction and expansion properties. For example, U.S. Pat. No. 5,816,943 is directed to a coating having a higher heat resistance than the cover material to prevent shallowing of dimples or dulling of dimple edges upon the coating application.
In addition, various golf ball compositions with purported improved light stability and durability have been disclosed. For example, U.S. Pat. No. 6,458,307 is directed to thermoplastic cover materials with a reported improvement in light stability, cut resistance, and abrasion resistance. U.S. Pat. No. 6,369,125 relates to crosslinkable thermoplastic compositions that can be melted and reformed and also have improved scuff and cut resistance over conventional balata covers.
While the efforts described above compensate for many problems associated with golf play during non-optimal conditions, no method of material has addressed all of the problems at once. In addition, most of the methods used to compensate for extreme temperature conditions involve the use of a special indicator, club, or warmer. Therefore, there remains a continuing need for novel compositions that solve temperature-related problems of conventionally-formed golf balls and golf clubs, e.g., resiliency and material degradation at non-optimal temperatures. In particular, it would be advantageous to provide a composition using trifunctional materials that provides heat resistance and dimensional stability, as well as improved resiliency, to golf ball and club components formed therefrom at non-optimal temperatures.